1. Field of the Invention
The present invention relates to multi-layer wiring substrates for use in electronic instruments such as various types of AV instruments, home electric appliances, communication instruments, computers and peripheral instruments thereof and, particularly, to a multi-layer wiring substrate in which a liquid crystal polymer layer is used as a portion of a dielectric layer.
2. Description of Related Art
Heretofore, a multi-layer wiring substrate for forming a mixed integrated circuit in which a predetermined electronic circuit is constructed by mounting thereon a multiple of active components such as a semiconductor element and the like, and passive components such as a capacitor element, a resistor element and the like have been formed by forming a vertical through-hole by means of a drill on a dielectric layer made up by impregnating an epoxy resin in glass cloth, forming a plurality of wiring conductors on an inside of the thus-formed through-hole and on a surface of the dielectric layer to form a wiring substrate and, then, laminating a multiple of the thus-formed wiring substrate.
Ordinarily, a present-day electronic instrument, as is represented by a mobile communication instrument, is requested to be small in size, thin, and light in weight, to have a high performance, high functionality, a high quality and high reliability. For this reason, electronic components such as a mixed integrated circuit and the like to be mounted on such electronic instrument has come to be requested to be small in size and of a high-density package. In order to meet such a requirement for the high-density package, minuteness of the wiring conductor, thinness of the dielectric layer and minuteness of the through-hole have come to be required also for the multi-layer wiring substrate which constitutes the electronic component. For this reason, in recent years, in order to allow the through-hole to be minute, laser processing which enables minute processing than drill processing has come to be employed.
However, in the dielectric layer made up of impregnating the epoxy resin in the glass cloth, there is a difficulty in providing a hole in the glass cloth by a laser whereby there is a limitation on minuteness of the through-hole and, further, there is a problem that it is difficult to form the through-hole having a uniform pore diameter due to the fact that a thickness of the glass cloth is not uniform.
In order to solve these problems, it has been proposed that the multi-layer wiring substrate in which an insulating backing material made up of either impregnating the epoxy resin in a non-woven fabric made of aramid resin fibers or coating an epoxy-type adhesive on a polyimide film was used for the dielectric layer.
However, the insulating backing material using the aramid non-woven fabric or the polyimide film is highly hygroscopic whereupon there is a problem that, when the insulating backing material which has absorbed moisture is subjected to a soldering reflow, the moisture absorbed therein is vaporized to generate a gas thereby causing a separation of the dielectric layer or other unfavorable phenomena. Further, the epoxy-type adhesive is high in a dielectric constant whereupon there is another problem that transmission characteristics thereof in a high frequency region are deteriorated.
In order to solve these problems, it has been studied to use a liquid crystal polymer as a material for the dielectric layer of the multi-layer wiring substrate. Since a layer comprising the liquid crystal polymer is constituted by rigid molecules whereupon these molecules have a structure such that they are orderly aligned to some extent and an attraction force between the molecules is strong, the layer exhibits high thermal resistance, a high Young""s modulus, high dimensional stability and a low hygroscopic property to have characteristics that there is no need of using a reinforcing material such as glass cloth therein and, further, it is excellent in a microfabrication property. Further, the layer has characteristics that, even in a high frequency region, it has a low dielectric constant and a low dielectric tangent and, also, an excellent high frequency property.
While making use of such characteristics of the liquid crystal polymer, Japanese Unexamined Patent Publication JP-A 8-97565 (1996) has proposed a multi-layer printed circuit substrate in which a plurality of circuit layers contain a first liquid crystal polymer and allow an adhesive layer which contains a second liquid crystal polymer having a lower melting point than that of the first liquid crystal polymer to be inserted therebetween. Further, Japanese Unexamined Patent Publication JP-A 2000-269616 (2000) has proposed a high-frequency circuit substrate in which a thermoplastic liquid crystal polymer film and a metallic foil were adhered with each other by the epoxy-type adhesive to form a liquid crystal polymer film which is then used as an electric dielectric layer.
However, in the multi-layer printed circuit substrate proposed by JP-A 8-97565, when the adhesive layer containing the liquid crystal polymer is inserted between a plurality of circuit layers and adhered them with one another by means of thermal compression bonding, due to the fact that the liquid crystal polymer is rigid to be incapable of moving into a fine dent formed on a surface of the circuit layer, there is a problem that it can not exert a sufficient anchor effect whereupon adhesiveness between the circuit layer and the adhesive layer is inferior to exhibit an insulation failure by a high temperature bias test.
Further, in the high-frequency circuit substrate proposed by JP-A 2000-269616, since a dielectric constant of the epoxy-type adhesive is different from that of the liquid crystal polymer to a great extent, by a small variation of thickness to be caused by a pressure to be applied at the time of lamination, there appears a problem that the transmission characteristics are deteriorated in the high frequency region, particularly, in a frequency region of 100 MHz or more. Further, since a film in which an orientation property of liquid crystal polymer molecules is corrupted is used, an attraction force between the liquid crystal polymer molecules becomes weak whereby coefficient of thermal expansion of liquid crystal polymer film is increased and, as a result, when the multi-layer wiring substrate is constituted by these substrates, there is a problem that a wiring failure is generated at a joint between a through-hole conductor and a wiring conductor therein by a temperature cycle test. Further, in accordance with a weak attraction force between the molecules, flexural strength becomes weak whereupon there is a problem that, when the wiring substrate is brought to be thinner than before by decreasing a thickness of the electric dielectric layer, a camber will be generated therein.
The invention has been attained to solve these problems of the prior art and has an object of providing a multi-layer wiring substrate having a high-density wiring and being excellent in soldering thermal resistance, insulating property, and high-frequency transmission characteristics.
The invention provides a multi-layer wiring substrate comprising:
a lamination of a plurality of dielectric layers which each comprise an organic material and are each provided with a wiring conductor of a metallic foil on at least one surface of upper and bottom surfaces of the respective dielectric layers, the wiring conductors between which the dielectric layer is disposed being electrically connected with each other via a through conductor formed in the dielectric layer, wherein the dielectric layers each individually are composed of a liquid crystal polymer layer and cladding layers comprising a polyphenyleneether-type organic substance, formed on upper and bottom surfaces of the liquid crystal polymer layer.
According to the invention, since the dielectric layer comprises the cladding layer which comprising the polyphenyleneether-type organic substance and are formed on a surface of the liquid crystal polymer layer, it becomes feasible to perform drilling processing for providing a fine through-hole and, as a result, a multi-layer wiring substrate having a high-density wiring can be formed. Further, since dielectric constant of the liquid crystal polymer layer and that of the cladding layer comprising the polyphenyleneether-type organic substance are the same to each other and, accordingly, frequency behaviors of both layers are the same thereby forming the multi-layer wiring substrate which is excellent in high frequency characteristics that a transmission characteristics in the high frequency region are not deteriorated regardless of a minor variation of thickness to be possibly generated at the time of lamination. Further, since the cladding layer comprising the polyphenyleneether-type organic substance exhibits a hydrophobic property similar to that of the liquid crystal polymer layer, resins of both layers are well compatible with each other and, therefore, are excellent in adhesiveness. Further, since the cladding layer has a random molecular structure and comprises a molecule which relatively easily moves by heat, the cladding layer can enter a fine dent formed on the surface of the liquid crystal polymer layer to sufficiently perform an anchor effect. As a result, the adhesiveness between the liquid crystal polymer and the cladding layer becomes favorable and there occurs no case in which an insulation failure is generated by a high temperate bias test. Further, since the liquid crystal polymer layer has a low hygroscopic property, there occurs no case in which, at the time of soldering reflow, water contained therein is vaporized to generate a gas or the dielectric layers are separated from one the other.
The invention provides a multi-layer wiring substrate comprising:
a lamination of a plurality of dielectric layers which each comprise an organic material and are each provided with a wiring conductor of a metallic foil on at least one surface of upper and bottom surfaces of the respective dielectric layers, the wiring conductors between which the dielectric layer is disposed being electrically connected with each other via a through conductor formed in the dielectric layer, wherein the dielectric layers each individually are composed of a liquid crystal polymer layer and cladding layers which are formed by laminating a first layer in which from 60% by volume to 80% by volume of inorganic insulating fillers are contained in a polyphenyleneether-type organic substance, a second layer in which from 40% by volume to 60% by volume of inorganic insulating fillers are contained in polyphenyleneether-type organic substance and a third layer in which from 20% by volume to 40% by volume of inorganic insulating fillers are contained in the polyphenyleneether-type organic substance in this order on each of upper and bottom surfaces of the liquid crystal polymer layer.
According to the invention, since the dielectric layers each individually comprise cladding layers formed by laminating a first layer in which from 60% by volume to 80% by volume of inorganic insulating fillers are contained in the polyphenyleneether-type organic substance, a second layer in which from 40% by volume to 60% by volume of the inorganic insulating fillers are contained in polyphenyleneether-type organic substance and a third layer in which from 20% by volume to 40% by volume of the inorganic insulating fillers are contained in the polyphenyleneether-type organic substance in this order on each of the upper and bottom surfaces of the liquid crystal polymer layer, coefficient of thermal expansion of the first layer which contacts the liquid crystal polymer layer in the cladding layer is approximate to that of the liquid crystal polymer layer and, as a result, no crack is generated in the cladding layer even by a temperature cycle test which includes a sharp temperature change whereupon a highly reliable multi-layer wiring substrate can be formed. Further, since a content of the inorganic insulating fillers in the third layer is set to be as small as from 20% by volume to 40% by volume, there neither occurs a case in which adhesiveness between the cladding layer and the wiring conductor is deteriorated to prevent the wiring conductor from being adhere-formed on the cladding layer, nor a case in which, when the dielectric layers are adhered to each other, adhesiveness between the cladding layers to form the dielectric layer is deteriorated to generate a separation between the dielectric layers causing a deterioration of an insulating property thereof.
The invention provides a multi-layer wiring substrate comprising:
a lamination of a plurality of dielectric layers which each comprise an organic material and are each provided with a wiring conductor of a metallic foil on at least one surface of upper and bottom surfaces of the respective dielectric layers, the wiring conductors between which the dielectric layer is disposed being electrically connected with each other via a through conductor formed in the dielectric layer, wherein the dielectric layers each individually are composed of a liquid crystal polymer layer and cladding layers each comprising a polyphenyleneether-type organic substance and another organic substance having a lower Young""s modulus than that of the former organic substance formed on upper and bottom surfaces of the liquid crystal polymer layer, and wherein, in the liquid crystal polymer layer, coefficient of thermal expansion thereof in a direction of layers is from xe2x88x9220 ppm/xc2x0 C. to 20 ppm/xc2x0 C. and Young""s modulus thereof is 2 GPa or more and, in the cladding layer, the Young""s modulus in a direction of layers is from 0.2 GPa to 1.5 GPa.
According to the invention, since the dielectric layer comprises the cladding layer comprising polyphenyleneether-type organic substance and another organic substance having Young""s modulus lower than that of the former organic substance formed on the surface of the liquid crystal polymer layer, it becomes feasible to drill-provide a fine through-hole and, as a result, the multi-layer wiring substrate having a high-density wiring can be formed. Further, since the dielectric constant of the liquid crystal polymer layer is approximate to that of the cladding layer, frequency behaviors of both layers are the same to each other thereby forming the multi-layer wiring substrate which is excellent in high frequency characteristics that a transmission characteristics in the high frequency region are not deteriorated regardless of a minor variation of thickness which is possibly generated at the time of lamination. Further, since the liquid crystal polymer layer has the coefficient of thermal expansion of from xe2x88x9220 ppm/xc2x0 C. to 20 ppm/xc2x0 C. in a direction of layers and Young""s modulus thereof of 2 GPa or more and the cladding layer has the Young""s modulus of from 0.2 GPa to 1.5 GPa in a direction of layers, when the cladding layer comprising the polyphenyleneether-type organic substance having a relatively large coefficient of thermal expansion undergoes a thermal expansion or a thermal contraction by a temperature change, since the Young""s modulus of this cladding layer is as low as from 0.2 GPa to 1.5 GPa, the thermal expansion and the thermal contraction of the cladding layer are bound with the liquid crystal polymer layer having a small coefficient of thermal expansion and a high Young""s modulus to allow the thermal expansion and thermal contraction of the cladding layer to be small. As a result, no crack is generated in the cladding layer even by a temperature cycle test which includes a sharp temperature change. Further, since it is not necessary to highly densely load the cladding layer with the inorganic insulating fillers, it is feasible that adhesiveness between the cladding layers themselves becomes favorable and, at the same time, there occurs no case in which the dielectric layers are separated from one another to deteriorate the insulating property thereof.
In the invention, it is preferable that a contact angle established between the liquid crystal polymer layer and triallyl isocyanurate is from 3xc2x0 to 50xc2x0.
According to the invention, the dielectric layer comprises the cladding layers comprising the polyphenyleneether-type organic substance formed on the upper and bottom surfaces of the liquid crystal polymer layer; on this occasion, since a molecule of the polyphenyleneether-type organic substance is not so rigid as that of a liquid crystal polymer and also does not exhibit a regular orientation, the former molecule is relatively easily movable and, as a result, even in a case in which the dielectric layers are allowed to be in a multi-layer form, adhesiveness of the dielectric layers among themselves becomes favorable whereupon a multi-layer wiring substrate which does not generate a separation of the dielectric layers from one another at a high temperature bias test that causes an insulation deficiency can be fabricated. Further, even in a case in which a wiring conductor is provided on the surface of the dielectric layer, the molecule of the polyphenyleneether-type organic substance moves into a fine dent formed on a surface of the wiring conductor thereby exerting a sufficient anchor effect whereupon adhesiveness between an insulating film and the wiring conductor becomes favorable, so that a separation between the insulating film and the wiring conductor that causes a wiring failure in the wiring conductor does not occur under conditions of high temperature and high moisture. Further, since dielectric constant of the liquid crystal polymer layer and that of the cladding layer comprising the polyphenyleneether-type organic substance are substantially the same with each other, frequency behaviors of both layers are the same with each other thereby forming the dielectric layer which is excellent in high frequency transmission characteristics that do not deteriorate transmission characteristics in a high frequency region regardless of a minor variation of thickness of the cladding layer to be possibly generated by pressure to be applied when the circuit conductor is adhered thereto. Further, since a wetting property of the polyphenyleneether-type organic substance to the liquid crystal polymer layer and that of triallyl isocyanurate are approximate to each other and also the contact angle of the liquid crystal polymer layer against triallyl isocyanurate is set to be from 3xc2x0 to 50xc2x0, the cladding layer comprising the polyphenyleneether-type organic substance is well compatible with the surface of the liquid crystal polymer layer whereupon adhesiveness between the liquid crystal polymer layer and the cladding layer comprising the polyphenyleneether-type organic substance can become strong and, as a result, a separation between dielectric layers does not occur by a thermal shock test such as a temperature cycle test and the like.
In the invention, it is preferable that a cross-sectional shape in a width direction of the wiring substrate provided on the dielectric layer is a trapezoid in which a first base of the wiring conductor on the side of the dielectric layer is shorter in length than a second base opposite to the first base and also an angle established between the first base and a side of the wiring conductor is from 95xc2x0 to 150xc2x0.
According to the invention, since a cross-sectional shape in a width direction of the wiring substrate provided on the dielectric layer is a trapezoid in which a first base of the wiring conductor on the side of the dielectric layer is shorter in length than a second base opposite to the first base and also an angle established between the first base and a side of the wiring conductor is from 95xc2x0 to 15xc2x0, when the wiring conductor is embedded in the cladding layer, it becomes feasible to embed the wiring conductor in the cladding layer in an easy manner.
In the invention, it is preferable that among sub-layers constituting the dielectric layer, a thickness x (xcexcm) of the cladding layer positioned between the shorter base of the wiring conductor and the liquid crystal polymer layer meets the following expression:
3 xcexcmxe2x89xa60.5Txe2x88x92txe2x89xa6xxe2x89xa60.5Txe2x89xa635 xcexcm (under the conditions of 8 xcexcmxe2x89xa6Txe2x89xa670 xcexcm, and 1 xcexcmxe2x89xa6txe2x89xa632 xcexcm),
wherein T is a distance (xcexcm) between the upper and bottom liquid crystal polymer layers, and t is a thickness (xcexcm) of the wiring conductor, respectively.
According to the invention, since a thickness x (xcexcm) of the cladding layer positioned between the shorter base of the wiring conductor and the liquid crystal polymer layer meets the following expression: 3 xcexcmxe2x89xa60.5Txe2x88x92txe2x89xa6xxe2x89xa60.5Txe2x89xa635 xcexcm, wherein T is a distance (xcexcm) between the upper and bottom liquid crystal polymer layers, and t is a thickness (xcexcm) of the wiring conductor, respectively, it is feasible to bring the difference between the distance between the shorter base of the wiring conductor and the liquid crystal polymer layer and the distance between the longer base of the wiring conductor and the liquid crystal polymer layer adjacent thereto to be as small as being less than t (xcexcm) and also to bring a variation of a dielectric dissipation factor in a periphery of the wiring conductor to be small and, as a result, deterioration of the transmission characteristics can be prevented.
In the invention, it is preferable that the liquid crystal polymer layer has an anisotropic dielectric property in which the dielectric constant becomes maximum in one direction of directions parallel to a plane of the liquid crystal polymer layer, and a degree of the anisotropic dielectric property represented by a ratio ∈x/∈y is from 1.2 to 2.0,
wherein ∈x is a dielectric constant in a direction in which the dielectric constant becomes maximum among directions parallel to the plane of the liquid crystal polymer layer, and ∈y is a dielectric constant in a direction orthogonal to the direction in which the dielectric constant becomes maximum among directions parallel to the plane of the liquid crystal polymer layer.
According to the invention, since the dielectric layer comprises the cladding layer comprising the polyphenyleneether-type organic substance formed on the surface of the liquid crystal polymer layer, it becomes feasible to drill the fine through-hole and, as a result, the multi-layer wiring substrate having a high-density wiring can be formed. Further, since the dielectric constant of the liquid crystal polymer layer and that of the cladding layer comprising the polyphenyleneether-type organic substance are low in the high frequency region, the multi-layer wiring substrate which is excellent in the transmission characteristics in the high frequency region can be formed. Further, since the cladding layer comprising the polyphenyleneether-type organic substance exhibits the hydrophobic property similar to that of the liquid crystal polymer layer, the compatibility thereof with the liquid crystal polymer layer is favorable whereby the adhesiveness thereof to the liquid crystal polymer layer becomes excellent. Further, since the cladding layer has a random molecular structure which permits it to move relatively easily by heat, when the wiring conductor is provided on the surface of the dielectric layer, the molecule which constitutes the cladding layer can enter the fine dent formed on the surface of the wiring conductor to exert a sufficient anchor effect and, as a result, adhesiveness between the wiring conductor and the cladding layer becomes favorable to cause no case in which an insulation failure is generated by a high temperature bias test. Further, since the liquid crystal polymer has a low hygroscopic property, there neither occur a case in which, at the time of soldering reflow, water contained therein is vaporized to generate gas, or the dielectric layers are separated from one the other.
According to the invention, since the liquid crystal polymer layer has an anisotropic dielectric property in which the dielectric constant becomes maximum in one direction of directions parallel to a plane of the liquid crystal polymer layer, and a degree of the anisotropic dielectric property represented by a ratio ∈x/∈y is from 1.2 to 2.0, wherein ∈x is a dielectric constant in a direction in which the dielectric constant becomes maximum among directions parallel to the plane of the liquid crystal polymer layer, and ∈y is a dielectric constant in a direction orthogonal to the direction in which the dielectric constant becomes maximum among directions parallel to the plane of the liquid crystal polymer layer, molecules of the liquid crystal polymer are regularly aligned to some extent to enhance an intermolecular force, coefficient of thermal expansion of the liquid crystal polymer layer can be decreased to a degree similar to that of a metal to be ordinarily used in the wiring conductor such as copper and, as a result, it becomes feasible to form the multi-layer wiring substrate in which wiring failure does not occur at a joint between the through conductor and the wiring conductor by the temperature cycle test.
In the invention, it is preferable that center line average roughness Ra of the upper and bottom surfaces of the liquid crystal polymer layer is from 0.05 xcexcm to 5 xcexcm.
In the invention, it is preferable that the cladding layer contains from 10% by volume to 70% by volume of inorganic insulating fillers.
In the invention, it is preferable that thickness of the cladding layer positioned between the liquid crystal polymer layer and the wiring conductor is from 3 xcexcm to 35 xcexcm.
Further, it is preferable that, in the multi-layer wiring substrate according to the invention, a first dielectric layer and a second dielectric layer adjacent to the first dielectric layer are laminated with each other such that an angle to be formed by directions in which respective dielectric constants of the liquid crystal polymer layers forming the first and second dielectric layers become maximum is from 50xc2x0 to 130xc2x0.
According to the invention, since the first dielectric layer and the second dielectric layer adjacent to the first dielectric layer are laminated with each other such that the angle to be formed by directions in which respective dielectric constants of the liquid crystal polymer layers forming the first and second dielectric layers become maximum is from 50xc2x0 to 130xc2x0, a particularly high flexural strength of the multi-layer wiring substrate that is expressed in a direction in which molecules are regularly aligned can be expressed in both longitudinal and transverse directions of the multi-layer wiring substrate. As a result, even when the multi-layer wiring substrate is brought to be thin, the multi-layer wiring substrate having no camber can be formed.
Further, in the invention, it is preferable that the polyphenyleneether-type organic substance is a thermosetting-type polyphenyleneether.
According to the invention, since the polyphenyleneether-type organic substance is set as the thermosetting-type polyphenyleneether, deformation by melting of the cladding layer comprising polyphenyleneether-type organic substance becomes small at the time of setting and also a case in which a position of the through conductor deviates from a position of the wiring conductor by heat-pressing at the time of forming the multi-layer wiring substrate by sequentially laminating the dielectric layers with one another are hardly to be generated whereupon the multi-layer wiring substrate which is excellent in conductive reliability can be obtained.
Further, in the invention, it is preferable that the cladding layer contains from 5% by volume to 60% by volume of an organic substance having a low Young""s modulus.
According to the invention, in this structure, since the cladding layer contains from 5% by volume to 60% by volume of the organic substance having the low Young""s modulus, the Young""s modulus of the cladding layer can easily be brought in a range of from 0.2 GPa to 1.5 GPa.
Further, in the invention, it is preferable that the organic substance having the low Young""s modulus contains from 20% by volume to 80% by volume of styrene-type organic substance.
According to the invention, in this constitution, since the organic substance having the low Young""s modulus contains from 20% by volume to 80% by volume of styrene-type organic substance, this styrene-type organic substance has a low dielectric constant and dielectric tangent whereupon the multi-layer wiring substrate which is excellent in the transmission characteristics at a high frequency of 100 MHz or more can be formed.
Further, in the invention, it is preferable that a total thickness of the cladding layers is from 10% to 70% of the thickness of the dielectric layers.
Further, according to the invention, in this constitution, since the total thickness of the cladding layers is from 10% to 70% of the thickness of the dielectric layers, adhesiveness thereof with the wiring conductor is favorable whereupon the multi-layer wiring substrate having high thermal resistance, a low hygroscopic property and high dimensional stability can be formed.